Comprehensive phylogenomic analyses re-write the evolution of parasitism within cynipoid wasps

Key to the North American tribes and genera of herb, rose, bramble, and inquiline gall wasps (Hymenoptera, Cynipoidea, Cynipidaesensu lato)

Robust keys exist for the family-level groups of Cynipoidea. However, for most regions of the world, keys to genera are not available. To address this gap as it applies to North America, a fully illustrated key is provided to facilitate identification of the tribes and genera of rose gall, herb gall, and inquiline gall wasps known from the region. For each taxon covered, a preliminary diagnosis and an updated overview of taxonomy, biology, distribution, and natural history are provided.

Re-establishment of the Nearctic oak cynipid gall wasp genus Feron Kinsey, 1937 (Hymenoptera: Cynipidae: Cynipini), including the description of six new species

The Nearctic cynipid oak gall wasp genus Feron Kinsey, comb. rev., is re-established with 34 species: F. albicomus (Weld, 1952), comb. nov., F. amphorus (Weld, 1926), comb. nov., F. apiarium (Weld, 1944), comb. nov., F. atrimentum (Kinsey, 1922), comb. nov., F. bakkeri (Lyon, 1984), comb. nov., F. caepula (Weld, 1926), comb. nov., F. californicum (Beutenmueller, 1911), comb. nov., F. clarkei (Bassett, 1890), comb. nov., F. comatum (Weld, 1952), comb. nov., F. crystallinum (Bassett, 1900), comb. nov., F. cylindratum (Kinsey, 1937), comb. nov., F. discale (Weld, 1926), comb. nov., F. discularis (Weld, 1926), comb. nov., F. dumosae (Weld, 1957), comb. nov., F. gigas (Kinsey, 1922), comb. nov., F. izabellae Melika, Nicholls & Stone, sp. nov., F. kingi (Bassett, 1900), comb. nov., F. parmula (Bassett, 1900), comb. nov., F. pattersonae (Fullaway, 1911), comb. nov., F. roberti Melika, Nicholls & Stone, sp. nov., F. rucklei Melika, Nicholls & Stone, sp. nov., F. scutellum (Weld, 1930), comb. nov., F. serranoae Pujade-Villar & Cuesta-Porta, sp. nov., F. splendens (Weld, 1919), comb. nov., F. stellare (Weld, 1926), comb. nov., F. stellulum (Burnett, 1974), comb. nov., F. sulfureum (Weld, 1926), comb. nov., F. syndicorum Pujade-Villar & Cuesta-Porta, sp. nov., F. tecturnarum (Kinsey, 1920), comb. nov., F. tetyanae Melika, sp. nov., F. tibiale Kinsey, 1937, comb. rev., F. tubifaciens (Weld, 1926), comb. nov., F. verutum Kinsey, 1937, comb. rev., and F. vitreum Kinsey, 1937, comb. rev. Most species are known only from the asexual generation; F. clarkei, F. comatum, and F. dumosae are known only from the sexual generation, while both generations are recognised for F. atrimentum, F. crystallinum, F. gigas, F. kingi, and F. pattersonae. Matching of alternate sexual and asexual generations is established for the first time for F. kingi and F. pattersonae (= Andricus pedicellatus (Kinsey, 1922), syn. nov.) based on molecular data (both cytb and ITS2 sequences). Morphological descriptions, re-descriptions, diagnoses, and a key to species are given, as well as data on DNA sequences, biology, phenology, and distribution.

The complete mitochondrial genome and gene rearrangements in a gall wasp species, Dryocosmus liui (Hymenoptera: Cynipoidea: Cynipidae)

Mitochondrial genomes (mitogenomes) have been widely used in comparative and evolutionary genomics, molecular evolution, phylogenetics, and population genetics, but very limited information is available for the family Cynipidae. In this report, we describe the mitogenome of Dryocosmus liui Pang, Su et Zhu, providing the first complete mitogenomic data for a cynipid gall wasp species. The mitogenome of D. liui is 16,819 bp in length, and contains the typical set of 37 genes. Two control regions were detected, with the second being a perfect inverted repeat of the major portion of the first. Gene rearrangements were found in transfer RNA (tRNA) genes, protein-coding genes (PCGs) and ribosomal RNA (rRNA) genes, compared with the putative ancestral mitogenome. Similar to two other Cynipidae species with mitogenome data available, D. liui has a novel tRNA gene cluster trnL1-trnI-trnL2-trnW-trnM-trnQ between nad1 and nad2. Phylogenetic analysis based on sequences of PCGs and rRNA genes with D. liui included obtained topologies identical to previous studies supporting the a relationship of (Cynipoidea , (Platygastroidea, Proctotrupoidea)) within the monophyletic Proctotrupomorpha and (Cynipidae, Figitidae), Ibaliidae) within the Cynipoidea.

Description of the first brachypterous Lonchidia species (Hymenoptera: Figitidae: Figitinae), with a key to European species

The male and female of a new species of Lonchidia Thomson, 1862, L. atypica Pujade-Villar & de Paz sp. nov., are described from the provinces of Salamanca and Cceres (Western Spain). Specimens were collected with a G-Vac suction sampler and pitfall traps from traditional almond and cherry orchards. The diagnostic characters of this species are: deep but short notauli, reaching only the anterior part of the mesoscutum, and brachypterous wings. Both sexes are illustrated and an identification key is proposed herein to differentiate the European species. The possibility that the male of L. clavicornis Thomson, 1862 corresponds to a different species is also discussed.

Biodiversity of hymenopteran parasitoids

Parasitoid wasps are the most successful group of insect parasitoids, comprising more than half the known diversity of Hymenoptera and probably most of the unknown diversity. This lifestyle has enabled them to be used as pest control agents conferring substantial economic benefits to global agriculture. Major lineages of parasitoid wasps include Ichneumonoidea, Ceraphronoidea, Proctotrupomorpha, and a number of aculeate families. The parasitoid lifestyle arose only once among basal Hymenoptera, in the common ancestor of the Orussidae and Apocrita some 200+ Ma ago. The ancestral parasitoid wasp was probably an idiobiont on wood-living beetle larvae. From this comparatively simple biology, Hymenoptera radiated into an incredible diversity of hosts and parasitoid lifestyles, including hyperparasitoidism, kleptoparasitoidism, egg parasitoidism, and polyembryony, in several instances co-opting viruses to subdue their hosts. Many lineages evolved beyond the parasitoid niche, becoming secondarily herbivorous or predatory nest provisioners and eventually giving rise to most instances of insect societies.

Key innovations and the diversification of Hymenoptera

The order Hymenoptera (wasps, ants, sawflies, and bees) represents one of the most diverse animal lineages, but whether specific key innovations have contributed to its diversification is still unknown. We assembled the largest time-calibrated phylogeny of Hymenoptera to date and investigated the origin and possible correlation of particular morphological and behavioral innovations with diversification in the order: the wasp waist of Apocrita; the stinger of Aculeata; parasitoidism, a specialized form of carnivory; and secondary phytophagy, a reversal to plant-feeding. Here, we show that parasitoidism has been the dominant strategy since the Late Triassic in Hymenoptera, but was not an immediate driver of diversification. Instead, transitions to secondary phytophagy (from parasitoidism) had a major influence on diversification rate in Hymenoptera. Support for the stinger and the wasp waist as key innovations remains equivocal, but these traits may have laid the anatomical and behavioral foundations for adaptations more directly associated with diversification.

Speciation in Nearctic oak gall wasps is frequently correlated with changes in host plant, host organ, or both

Quantifying the frequency of shifts to new host plants within diverse clades of specialist herbivorous insects is critically important to understand whether and how host shifts contribute to the origin of species. Oak gall wasps (Hymenoptera: Cynipidae: Cynipini) comprise a tribe of ∼1000 species of phytophagous insects that induce gall formation on various organs of trees in the family Fagacae-primarily the oaks (genus Quercus; ∼435 sp.). The association of oak gall wasps with oaks is ancient (∼50 my), and most oak species are galled by one or more gall wasp species. Despite the diversity of both gall wasp species and their plant associations, previous phylogenetic work has not identified the strong signal of host plant shifting among oak gall wasps that has been found in other phytophagous insect systems. However, most emphasis has been on the Western Palearctic and not the Nearctic where both oaks and oak gall wasps are considerably more species rich. We collected 86 species of Nearctic oak gall wasps from most of the major clades of Nearctic oaks and sequenced >1000 Ultraconserved Elements (UCEs) and flanking sequences to infer wasp phylogenies. We assessed the relationships of Nearctic gall wasps to one another and, by leveraging previously published UCE data, to the Palearctic fauna. We then used phylogenies to infer historical patterns of shifts among host tree species and tree organs. Our results indicate that oak gall wasps have moved between the Palearctic and Nearctic at least four times, that some Palearctic wasp clades have their proximate origin in the Nearctic, and that gall wasps have shifted within and between oak tree sections, subsections, and organs considerably more often than previous data have suggested. Given that host shifts have been demonstrated to drive reproductive isolation between host-associated populations in other phytophagous insects, our analyses of Nearctic gall wasps suggest that host shifts are key drivers of speciation in this clade, especially in hotspots of oak diversity. Although formal assessment of this hypothesis requires further study, two putatively oligophagous gall wasp species in our dataset show signals of host-associated genetic differentiation unconfounded by geographic distance, suggestive of barriers to gene flow associated with the use of alternative host plants.

New herb gall wasps from Iran (Hymenoptera: Cynipidae)

Five new gall wasp species, Aulacidea koeiana Melika, Tavakoli & Stone, sp. nov., A. lorestanica Melika, Tavakoli & Stone, sp. nov., A. piroziae Melika, Stone & Pujade-Villar, sp. nov., Phanacis strigosa Melika, Stone & Tavakoli, sp. nov., P. tavakolii Melika, Stone & Pujade-Villar, sp. nov. are described from Lorestan, Iran. Descriptions, diagnoses, plus information on biology and host associations are given for all new species, and we provide the first description of the male of Isocolus beheni Melika & Karimpour, 2008.  

Novel Gene Rearrangements in the Mitochondrial Genomes of Cynipoid Wasps (Hymenoptera: Cynipoidea)

Cynipoidea is a medium-sized superfamily of Hymenoptera with diverse lifestyles. In this study, 16 mitochondrial genomes were newly sequenced, 11 of which were the first obtained mitochondrial genomes in the family Liopteridae and four subfamilies (Anacharitinae, Aspicerinae, Figitinae, and Parnipinae) of Figitidae. All of the newly sequenced mitogenomes have unique rearrangement types within Cynipoidea, whereas some gene patterns are conserved in several groups. nad5-nad4-nad4L-nad6-cytb was remotely inverted and two rRNA genes were translocated to nad3 downstream in Ibaliidae and three subfamilies (Anacharitinae, Eucoilinae, and Parnipinae within Figitidae); two rRNA genes in Aspicerinae, Figitinae, and Liopteridae were remotely inverted to the cytb-nad1 junction; rrnL-rrnS was translocated to the cytb-nad1 junction in Cynipidae. Phylogenetic inference suggested that Figitidae was a polyphyletic group, while the Ibaliidae nested deep within Cynipoidea and was a sister-group to the Figitidae. These results will improve our understanding of the gene rearrangement of the mitogenomes and the phylogenetic relationships in the Cynipoidea.

Global phylogeny of the inquilinous gall wasp tribe Synergini (Hymenoptera: Cynipoidea: Cynipidae): first insights and establishment of a new cynipid tribe

Previous phylogenetic studies of the tribe Synergini were focused on Palaearctic material, in which the genus Synergus was recovered as monophyletic, despite evidence of non-monophyly when global sampling is considered. A global molecular phylogeny of Synergini, including sequenced material from Nearctic and Neotropical realms, is presented herein for the first time. We assembled DNA data for 120 specimens: 104 representing all genera belonging to Synergini, except for the rare monospecific genus Agastoroxenia (ingroup), and 16 belonging to five other tribes of Cynipidae (outgroup). We obtained sequences for four genes: cytochrome c oxidase subunit I (COI), cytochrome b (Cytb), 28S region D2 (28S D2) and 28S region D3 (28S D3). The evaluated analyses support the non-monophyly of both Saphonecrus and Synergus (with Nearctic and Neotropical Synergus resolved into three clades separated from the Palaearctic species), as well as the monophyly of the rest of the genera in Synergini. Furthermore, the results suggest that neither Saphonecrus s.s. nor Synergus s.s. are present in the New World. The future challenges to separate the clades of Saphonecrus and Synergus into new taxa are discussed. Lastly, Rhoophilus was shown to belong to a new tribe, Rhoophilini trib. nov., on the basis of molecular, morphological and biological data.

Ultraconserved elements-based systematics reveals evolutionary patterns of host-plant family shifts and phytophagy within the predominantly parasitoid braconid wasp subfamily Doryctinae

Phytophagy has promoted species diversification in many insect groups, including Hymenoptera, one of the most diverse animal orders on Earth. In the predominantly parasitoid family Braconidae, an association with insect-induced, plant galls in angiosperms have been reported in three subfamilies, but in particular in the Doryctinae, where it has been recorded to occur in species of ten genera. Allorhogas Gahan is the most species-rich of these genera, with its species having different phytophagous strategies. Here we conducted a comprehensive phylogenomic study for the doryctine gall-associated genera, with an emphasis on Allorhogas, using ultraconserved elements (UCEs). Based on this estimate of phylogeny we: (1) evaluated their taxonomic composition, (2) estimated the timing of origin of the gall-associated clade and divergence of its main subclades, and (3) performed ancestral state reconstruction analyses for life history traits related to their host-plant association. Our phylogenetic hypothesis confirmed Allorhogas as polyphyletic, with most of its members being nested in a main clade composed of various subclades, each comprising species with a particular host-plant family and herbivorous feeding habit. The origin of gall-association was estimated to have occurred during the late Oligocene to early Miocene, with a subsequent diversification of subclades during the middle to late Miocene and Pliocene. Overlap in divergence timing appears to occur between some taxa and their host-associated plant lineages. Evolution of the feeding strategies in the group shows "inquilinism-feeding" as the likely ancestral state, with gall-formation in different plant organs and seed predation having independently evolved on multiple occasions.

Chromosomes of three gall wasps of the tribe Aylacini (Hymenoptera, Cynipidae)

Chromosomes of two species of the tribe Aylacini (Cynipidae), Isocolus jaceae (Schenck, 1863) and I. scabiosae (Giraud, 1859) (both have 2n = 18) were studied for the first time. In addition, 2n = 20 is confirmed in a member of the same tribe, Aulacidea hieracii (Bouché, 1834). All chromosomes of these gall wasps are biarmed; however, they gradually decrease in size in the case of A. hieracii, whereas a pair of large metacentrics is characteristic of karyotypes of both Isocolus Förster, 1869 species. Chromosomes of the two latter gall wasps are either metacentric or submetacentric, but elements with lower centromeric indices prevail in the karyotype of A. hieracii. Chromomycin A₃ (CMA₃)/DAPI staining revealed single CMA₃-positive bands on a particular pair of chromosomes of all species, and these bands apparently refer to the nucleolus organizing regions (NORs). However, localization of CMA₃-positive bands differs substantially between the studied members of Isocolus and Aulacidea Ashmead, 1897. Together with normal haploid and diploid mitotic divisions, several metaphase plates with 2n = 17 containing a peculiar dicentric chromosome were found in a single male specimen of I. scabiosae; this appears to be the first report of an obvious dicentric in the order Hymenoptera in general. Certain aspects of the chromosome diversity and karyotype evolution within the family Cynipidae and the tribe Aylacini in particular are briefly discussed.

Comprehensive phylogenomic analyses re-write the evolution of parasitism within cynipoid wasps

BACKGROUND

Parasitoidism, a specialized life strategy in which a parasite eventually kills its host, is frequently found within the insect order Hymenoptera (wasps, ants and bees). A parasitoid lifestyle is one of two dominant life strategies within the hymenopteran superfamily Cynipoidea, with the other being an unusual plant-feeding behavior known as galling. Less commonly, cynipoid wasps exhibit inquilinism, a strategy where some species have adapted to usurp other species' galls instead of inducing their own. Using a phylogenomic data set of ultraconserved elements from nearly all lineages of Cynipoidea, we here generate a robust phylogenetic framework and timescale to understand cynipoid systematics and the evolution of these life histories.

RESULTS

Our reconstructed evolutionary history for Cynipoidea differs considerably from previous hypotheses. Rooting our analyses with non-cynipoid outgroups, the Paraulacini, a group of inquilines, emerged as sister-group to the rest of Cynipoidea, rendering the gall wasp family Cynipidae paraphyletic. The families Ibaliidae and Liopteridae, long considered archaic and early-branching parasitoid lineages, were found nested well within the Cynipoidea as sister-group to the parasitoid Figitidae. Cynipoidea originated in the early Jurassic around 190 Ma. Either inquilinism or parasitoidism is suggested as the ancestral and dominant strategy throughout the early evolution of cynipoids, depending on whether a simple (three states: parasitoidism, inquilinism and galling) or more complex (seven states: parasitoidism, inquilinism and galling split by host use) model is employed.

CONCLUSIONS

Our study has significant impact on understanding cynipoid evolution and highlights the importance of adequate outgroup sampling. We discuss the evolutionary timescale of the superfamily in relation to their insect hosts and host plants, and outline how phytophagous galling behavior may have evolved from entomophagous, parasitoid cynipoids. Our study has established the framework for further physiological and comparative genomic work between gall-making, inquiline and parasitoid lineages, which could also have significant implications for the evolution of diverse life histories in other Hymenoptera.